The photoresist stripper/plasma etch residue cleaner art is replete with numerous references to compositions containing either a polar solvent or an alkanolamine compound, or both. The presence of an alkanolamine in photoresist stripper compositions has been judged to be essential to effectively remove cross-linked resist films. However, alkanolamine-type photoresist strippers sometimes have a serious problem of corrosion, especially with aluminum substrates.
It is believed that the corrosion is caused in part by the ionization of water with the alkanolamine in post-stripping water rinse, as residual stripper solution may be retained on the substrate surface and/or substrate carrier after the stripping step. In other words, the alkanolamine component of the stripper composition does not corrode the substrate by itself, but can trigger water to cause the corrosion.
To solve this problem, an intermediate rinse step with an organic solvent (e.g., isopropyl alcohol) has been used between the stripping step and the post-stripping rinse with water. However, such intermediate rinses are not necessarily desirable because overall stripping operation becomes more complicated and, furthermore, an additional solvent waste is produced. Accordingly, if alkanolamine-containing strippers are to be further employed, there is a need to solve this corrosion problem without generation of intermediate organic solvent wastes.
In addition, other mechanisms of metal corrosion are known. For example, metal halides, such as aluminum chloride, tend to be generated as plasma-etch by-products. Metal halides may cause corrosion of substrates when contacted with water from a water rinse following the cleaning process. Another corrosion mechanism is observed especially with alloys such as Al--Cu--Si during cleaning or in a post-clean rinse process. This type of corrosion is usually observed locally and is referred to as pitting. Pitting is thought to be caused by the galvanic type of the electrochemical reaction between two metals which have different electronegativities.
The present invention provides a solution for all the above-described types of corrosion.
Furthermore, during anisotropic plasma etching processes for via contacts, metal patterns, and passivation openings, "sidewall residues" are frequently deposited on the resist sidewall. After the oxygen plasma ashing of photoresist films, these residues become metal oxides. Incomplete removal of these residues interfere with the pattern definition and/or complete filling of via holes.
Several different chemistries have been identified for removing the post-etch residues, particularly the metal oxide type. For example, alkaline aqueous developers such as those containing tetramethylammonium hydroxide (TMAH) are known to attack aluminum. Thus, an aluminum oxide residue can be etched away with TMAH. However, other types of the post-etch residues associated with multi-metal systems such as Al--Si--Cu cannot be so easily removed with TMAH. TMAH also is ineffective on residues formed from polysilicon plasma etch processes.
The metal oxide type sidewall residues can also be removed with: (1) a mixture of hydrofluoric acid and ethylene glycol ether, or (2) a mixture of nitric acid, acetic acid, and hydrofluoric acid. These solutions require extreme process control to prevent excessive attack of critical metal and oxide layers. In some device structures, these solutions are not useful because of their nonselective attack mechanisms.
Wai M. Lee described at Interconnects, Contact Metallization and Multilevel Metallization Symposium (183rd Spring Meeting of The Electrochemical Society) in Honolulu, HI, May 16-21, 1993, that a hydroxylamine-containing amine/water-based stripper composition can remove some kinds of the sidewall residues. Although hydroxylamine has a potential to enhance the stripper ability and/or the metal corrosion inhibition, it is not stable upon heating. Therefore, the use of hydroxylamine is not recommended, especially when used in a highly alkaline medium.
Accordingly, hydroxylamine is not suitable for use in stripping of photoresist films or cleaning of the post-etch residues at higher temperatures.
Illustrative of references suggesting photoresist stripping or plasma-etch residue cleaning compositions containing a polar solvent and/or an alkanolamine compound are the following:
U.S. Pat. No. 4,617,251, which issued to Sizensky et al. on Oct. 14, 1986, teaches a positive photoresist stripping composition containing: (A) selected amine compound (e.g., 2-(2-aminoethoxy) ethanol, 2-(2-aminoethylamino)ethanol, and mixtures thereof) and (B) selected polar solvents (e.g., N-methyl-2-pyrrolidinone, tetrahydrofurfuryl alcohol, isophorone, dimethyl sulfoxide, dimethyl adipate, dimethyl glutarate, sulfolane, gamma-butyrolactone, N,N-dimethylacetamide and mixtures thereof). The reference further teaches that water as well as dyes or colorants, wetting agents, surfactants and antifoamers may be added into this composition.
U.S. Pat. No. 5,279,791, which issued to Lee on Jan. 18, 1994, teaches a stripping composition for removing resists from substrates containing (A) hydroxylamine (e.g., NH.sub.2 OH); (B) at least one alkanolamine; and optionally (C) at least one polar solvent.
European Patent Application No. 647884 assigned to J.T. Baker Inc. discloses nonaqueous photoresist stripper composition comprising (i) a stripping solvent (e.g. N-methyl-2-pyrrolidinone), (ii) a nucleophilic amine (e.g., monoethanolamine), and (iii) a reducing agent such as salicyl aldoxime, gallic acid, and gallic acid esters.
European Patent Application No. 596515 assigned to JT Baker, Inc. discloses an alkaline photoresist stripping composition comprising a solvent, a nucleophilic amines (e.g., 1-amino-2-propanol, 2-aminoethanol), and a non-nitrogen containing weak acid
German Published Patent Application No. DE3828513, which issued to Schulz on Mar. 1, 1990, teaches a positive and negative photoresist stripper composition containing (A) an aprotic polar solvent (e.g., 1,3-dimethyl-2-imidazolidinone or 1,3-dimethyl-tetrahydropyrimidinone); and (B) an organic base (e.g., alkanolamine).
Japanese Published Patent Application No. 1-081949, which issued to K. Matsumoto (Asahi Chemical) on Mar. 28, 1989, teaches a positive-working photoresist stripper composition containing (A) gamma-butyrolactone, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide or N-methyl-2-pyrrolidinone; (B) an amino alcohol (e.g., N-butyl-ethanolamine and N-ethyldiethanolamine); and (C) water.
Japanese Published Patent Application No. 4-350660, which issued to H. Goto et al. (Texas Instruments, Japan and Kanto Chemical, Inc.) on Dec. 4, 1992, teaches a stripper for positive photoresists comprising (A) 1,3-dimethyl-2-imidazolidinone, (B) dimethylsulfoxide and (C) a water-soluble amine (e.g., monoethanolamine or 2-(2-aminoethoxy)ethanol wherein the amount of the water-soluble amine is 7-30% by weight.
Japanese Published Patent Application No. 7-271057, which was published on Oct. 20, 1995, and is assigned to Tokyo Ohka Kogyo, teaches positive photoresist compositions that contain N,N-diethylhydroxyamine. Preferred formulations also contained either alkanolamines (e.g., monoethanolamine); water-miscible organic solvents (e.g. N-methyl-2-pyrrolidinone); water; additives (e.g., hydroxy aromatic compounds or triazole compounds); or carboxylic group-containing organic compounds, or certain combinations thereof. Salicyl alcohol is one of the preferred hydroxy aromatic compounds.
Japanese Published Patent Application No. 7-271057 does suggests the addition of carboxylic acid to an admixture of a water-miscible polar solvent and an alkanolamine for the application to photoresist stripping composition or plasma-etch residue cleaning composition. However, that reference requires the presence of a hydroxylamine compound, N,N-diethylhydroxylamine (DEHA), to achieve its desired performance.
Likewise European Patent Application No. 596515 does discloses an admixture of a solvent, an alkanolamine and a non-nitrogen containing weak acid in its formulation. However, this composition does not contain water which is essential in the removal of some kinds of plasma etch residues.
The stripping and cleaning composition of the present invention, on the other hand, is effective in removing a wide variety of both organic polymeric materials and plasma-etch residues. The inventor has found that some types of corrosion inhibitors can prevent metal corrosion without any reduction in the stripping rate of photoresist, or any reduction in the effectiveness of removing plasma etch residues. The present formulation provides a superior balance of various functional and economic requirements, including excellent prevention of metal contamination of substrate surfaces, and favorable material cost for the desired corrosion inhibition effect.